Methylammonium-Mediated Crystallization of Cesium-Based 2D/3D Perovskites toward High-Efficiency Light-Emitting Diodes

Two-dimensional (2D)/three-dimensional (3D) perovskites have been successfully applied in high-efficiency light-emitting diodes (LEDs) because of their large exciton binding energy (E_b) caused by the quantum and dielectric confinements. Thermal annealing and antisolvent treatments are usually executed in order to promote the crystallization and film quality of perovskites, which add complexity to the device fabrication process. Here, the cesium-based 2D/3D perovskite was prepared by introducing ammonium halide benzamidine hydrochloride (BMCl) as the additive. By further introducing an appropriate amount of MABr and PbBr₂, BM₂(Cs_1–xMA_xPbBr₃)_n−1PbBr₄ crystals can be formed rapidly without any additional treatments, while inhibiting the formation of the unfavorable Cs₄PbBr₆ phase. The optimized 2D/3D perovskite-based LEDs achieved a maximum luminance of 12 367 Cd/m², a current efficiency of 17.4 Cd/A, and an external quantum efficiency of 5.2%. Our results suggest that appropriate perovskite crystallization can be achieved at room temperature by the regulation of precursor solution, making the perovskite crystallization process easier to control with reduced processing complexity.